fossilfandomcom-20200214-history
Juravenator
Juravenator is a genus of small (70 cm long) coelurosaurian dinosaur, which lived in the area which would someday become the Jura mountains of Germany, 150 million years ago. Discovery and naming In the summer of 1998, the Jura-Museum Eichstätt at Eichstätt organised a paleontological expedition to the nearby chalk quarry of Schamhaupten. Near the end of the planned excavations, two volunteers, Klaus-Dieter Weiß and his brother Hans-Joachim Weiß, found a chalk plate in which clear vertebrate remains were visible. A first preparation uncovered the head of a small theropod. However, due to the vulnerability of the bones, removing the hard calcium silicate matrix was slow and expensive. To see whether it was worthwhile to proceed, a CT-scan of the fossil was made. This seemed to show that only the neck and a small part of the rump were still present and accordingly the preparation was discontinued. In 1999 the find was reported in the scientific literature by Günther Viohl.1 By 2001 the fossil had generated some publicity and was nicknamed Borsti in the German press, a name commonly given to bristle-haired dogs, on the assumption the creature was endowed with bristly protofeathers. In 2003, the new director of the museum, Martina Kölbl-Ebert, decided to finish the preparation. Preparator Pino Völkl then discovered, during seven hundred hours uncovering the remaining bones, that almost the entire skeleton was present. In 2006 the type species Juravenator starki was named and described by Ursula Göhlich and Luis Chiappe. The generic name is derived from the Jurassic Bavarian Jura Mountains, and a Latin venator, "hunter". The specific name honours the Stark family, owners of the quarry.2 The holotype, JME Sch 200, was found in the Malm Epsilon 2, a marl layer of the Painten Formation dating to the late Kimmeridgian, about 151 to 152 million years old. As the bones were accessed from below — the specimen having landed on its back on the seafloor3 — and the plate was not split further, a counterslab is lacking. The fossil consists of an almost complete articulated skeleton with skull of a juvenile individual. Only the tail end is missing. In small areas impressions or remains of the soft parts are present. The fossil was considered the most complete specimen of a non-avian theropod ever found in Europe. Description Juravenator was originally published as a member of the family Compsognathidae, making it a close relative of Sinosauropteryx and Sinocalliopteryx, for which there is fossil evidence of a downy, feather-like covering, yet a patch of fossilized Juravenator skin shows only normal dinosaur scales, with no sign of feathers at all. While it may simply have never had feathers, paleontologist Mark Norell suggest that the presence of scales on the tail of Juravenator could mean a number of things http://www.chron.com/disp/story.mpl/nation/3724592.html: * Juravenator could have lost its feathers secondarily on at least some parts of its body, like some modern, partially featherless birds. * Feathers could have evolved more than once in different types of dinosaur. * Since the only known Juravenator skeleton is juvenile, it could be that this species only grew a significant covering of feathers as they aged, or lost feathers seasonally. * The feathers might simply have not been preserved in this specimen. "Feathers are really just difficult things to preserve," Norell says, though Luis Chiappe, director of the Dinosaur Institute at the Natural History Museum of Los Angeles County points out that the fossil skin does not show the follicles normally associated with dinosaur skin that has lost its feathers. Xu, Xing. (2006) "Scales, feathers, and dinosaurs". "Nature", 440: 287-288. 16 March 2006 Additionally, subsequent studies have found problems with the initial study that placed Juravenator among the compsognathids. Rather than grouping it with Sinosauropteryx and other compsognathids, Butler et al. found that it was not a compsognathid, but rather a basal member of the group Maniraptora. Studies conflict on whether or not compsognathids belong to this later group or are more primitive, though all other maniraptoran skin impressions also show evidence of feathers. The fossil, found in 1998 by amateur paleontologist Klaus-Dieter Weiß in a lime pit near Eichstätt, had been nicknamed Borsti in German, a name commonly given to bristle-haired dogs, on the assumption the creature was endowed with bristly protofeathers. Classification References *Butler, R.J., and Upchurch, P. (2007). "Highly incomplete taxa and the phylogenetic relationships of the theropod dinosaur Juravenator starki." Journal of Vertebrate Paleontology, 27(1): 253-256. *Göhlich, U.B., and Chiappe, L.M. (2006). "A new carnivorous dinosaur from the Late Jurassic Solnhofen archipelago." Nature, 440: 329-332. External links *An image of Juravenator from National Geographic Category:Jurassic dinosaurs Category:Dinosaurs of Europe Category:Solnhofen fauna compsognathids